In recent years, so-called micromachines have been proposed which are several millimeters or smaller in size, and various research and developing efforts have been made for introducing micromachines into actual use.
Heretofore known as the methods of driving micromachines are the cable method wherein a cable is used for supplying energy (electric power) and control signals from outside to the body of the machine which has various actuators, and the cableless method wherein control signals only are wirelessly fed from outside to the machine body which is internally provided with a battery or like energy source.
When having the cable, the micromachine has an energy source outside of its body. This leads to the advantage of making the machine body compact and affording greater freedom in designing the micromachine since the amount of drive energy is not limited, whereas the cable which is indispensable to the supply of energy imposes limitations on the range of movement of the machine as well as on the motion thereof.
When cableless, on the other hand, the micromachine is movable without limitations, but the need to mount the energy source thereon makes the machine body larger and heavier to impair the contemplated function of the micromachine.
Accordingly, we have made research on cableless micromachines which have no energy source mounted on the machine body and to which energy is applied from outside cablelessly by applying rays or like electromagnetic waves to the machine body. In this case, the surface of the machine body is covered with photoelectromotive devices such as solar cells for converting the electromagnetic waves applied to an electric power.
However, micromachines are compacted to the greatest possible extent and are therefore limited in the area for receiving electromagnetic waves (light receiving area). Moreover, solar cells or like photoelectromotive devices are presently as low as up to about 20 to about 30% in electric power conversion efficiency. Accordingly, if the micromachine is heavily loaded for the function to be performed, it is likely that the electromotive force of the photoelectromotive devices will be insufficient to meet the power requirement. Further when the micromachine passes through a location where rays are not accessible, a temporary power failure will occur.
In the case where the cableless micromachine is inserted into a pipe, for example, for inspecting the pipe wall with a supply of electromagnetic waves to the micromachine within the pipe, the source for emitting electromagnetic waves is installed at the inlet of the pipe, so that the intensity of energy of electromagnetic waves reaching the micromachine decreases with the inward travel of the micromachine. Even if the micromachine can be moved to a predetermined position, the electric power available is likely to be insufficient for the machine to perform the intended operation, such as pipe wall inspection, at the position.
Although a majority of light energy remaining unconverted to power by the photoelectromotive devices changes into heat, there arises the problem that the heat generated is confined within the micromachine because the micromachine has a very small outer wall surface area for dissipating heat and highly integrated mechanisms and electronic circuits. This results in a rise in the internal temperature to lower the power conversion efficiency of the photoelectromotive devices and is also likely to entail a malfunction of the electronic circuit for performing the contemplated function or operation of the micromachine.